1. Field of the Invention
This invention concerns a thermal oil recovery method utilizing in-situ combustion and water in a method which permits efficient recovery of heavy oil from permeable, heavy oil-bearing reservoirs.
2. Background and Prior Art
It has been proposed to recover oil, in the nature of heavy viscous oils, from a subterranean reservoir by a method which is commonly known as in-situ combustion. In this method, an oxygen-containing gas is injected into the reservoir through an injection well with ignition of oil within the adjacent reservoir initiated by suitable means for establishing a combustion front. The reservoir is usually provided with one or more production wells for the production of oil. As the flow of oxygen-containing gas to the reservoir is continued, the combustion front is moved from the injection well toward the production wells. The heat generated by burning reduces the viscosity of the oil which is displaced before the combustion front toward the production wells from which the oil is recovered. The combustion front in displacing the mobile oil before it in the reservoir uses the residual carbonaceous deposit as fuel.
In these processes, the gaseous combustion products and light hydrocarbons are considerably lighter than the oil and water present in the reservoir and thus, because of gravity segregation, tend to rise to the top of the reservoir when vertical communication exists. Consequently, these products channel through the top of the formation to the producing well overriding a major portion of the reservoir and contacting only a small fraction of the reservoir oil. This behavior results in inefficient oil recovery and low vertical sweep efficiency.
Furthermore, in such in-situ combustion processes, large quantities of heated rock are left behind in the reservoir. This heat is therefore lost, which greatly reduces the thermal efficiency of the process.
Our improved invention provides a substantial advance in recovering heavy oil from permeable, heavy oil-bearing reservoirs utilizing in-situ combustion.